1. Field of the Invention
The present invention relates to a cylinder head structure in a multi-cylinder engine, including a collecting exhaust port which is comprised of exhaust port sections extending from a plurality of combustion chambers arranged along a cylinder array, respectively, the port sections being integrally collected together in an exhaust collecting section defined within a cylinder head.
2. Description of the Related Art
In general, an exhaust port defined in a cylinder head in a multi-cylinder engine serves only to collect exhaust gases discharged from a plurality of exhaust valve bores in the same cylinder in the cylinder head, and the collection of the exhaust gases discharged from the cylinders is carried out in a separate exhaust manifold coupled to the cylinder head.
On the contrary, there is a cylinder head structure which is known from Japanese Patent No. 2709815, in which the collection of the exhaust gases discharged from the cylinders is carried out in the cylinder head without using a separate exhaust manifold. In such cylinder head structure, the entire periphery of collecting exhaust ports integrally collected together within the cylinder head is surrounded by a water jacket to enhance the cooling efficiency, so that the durability can be ensured, even if the cylinder head is made using a material poor in heat resistance.
However, the cylinder head structure described in Japanese Patent No. 2709815 suffers from a problem that the cylinder head is large-sized because the entire side surface of the cylinder head provided with an exhaust collecting section projects in a large amount sideways from a mating surface of the cylinder head with a cylinder block. Further, the structure suffers from a problem that the cylinder head is large-sized to hinder the compactness of the entire engine and increase the vibration, because the entire periphery of the collecting exhaust ports integrally collected together within the cylinder head is surrounded by the water jacket. Moreover, a collecting exhaust port forming core and a water jacket forming core each having a complicated shape cannot be assembled intact. It is required that either one of the cores or both the cores be divided into parts and assembled. For this reason, there is a possibility that the structures of the cores may further be complicated, not only causing an increase in cost, but also causing a reduction in accuracy of the completed cylinder head.
Accordingly, it is an object of the present invention to ensure that the cylinder head including the collecting exhaust port integrally provided therein can be made as compact as possible, and the exhaust collecting section can be formed by molding, while avoiding the complication of the core structure.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a cylinder head structure in a multi-cylinder engine, comprising a collecting exhaust port which is comprised of exhaust port sections extending from a plurality of combustion chambers arranged along a cylinder array, respectively, and integrally collected together in an exhaust collecting section defined within a cylinder head, wherein the structure includes a protrusion provided on a side surface of the cylinder head to project outside a side surface of a cylinder block to which the cylinder head is coupled, the protrusion projecting outwards in a largest amount in the exhaust collecting section.
With the above arrangement, the protrusion projecting outwards from the side surface of the cylinder head projects outwards in the largest amount in the exhaust collecting section. Therefore, the size of the protrusion can be reduced to contribute to the compactness of the cylinder head, as compared with a structure including a water jacket provided outside the exhaust collecting section. Moreover, the weight of the protrusion is decreased and hence, the vibration of the cylinder head can be alleviated.
According to a second aspect and feature of the present invention, there is provided a cylinder head structure in a multi-cylinder engine, comprising a collecting exhaust port which is comprised of exhaust port sections extending from a plurality of combustion chambers arranged along a cylinder array, respectively, and integrally collected together in an exhaust collecting section defined within a cylinder head, wherein the structure includes a protrusion formed on a side surface of the cylinder head to project in an arch shape outside a side surface of a cylinder block to which the cylinder head is coupled, and the exhaust collecting section is formed, so that no water jacket is interposed between a side wall of the protrusion and the exhaust collecting section.
With the above arrangement, the exhaust collecting section is formed with no water jacket interposed between the exhaust collecting section and the side wall of the protrusion projecting in the arch shape from the side surface of the cylinder head. Therefore, the size of the protrusion can be reduced to contribute to the compactness of the cylinder head, as compared with a structure including a water jacket provided outside the exhaust collecting section. Moreover, the rigidity of the cylinder head can be increased by the arch-shaped protrusion. Additionally, no water jacket is provided outside the exhaust collecting section and hence, a core for forming the collecting exhaust port can be inserted into a core for forming a water jacket at the time of casting of the cylinder head, thereby facilitating the casting of the cylinder head without employment of a means causing an increase of cost such as the division of the cores into parts. Further, the weight of the protrusion is decreased and hence, the vibration of the cylinder head can be alleviated.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.